[Beowulf] Power savings at idle, especially Tyan S2466N-MPX

[David Mathog]

The administration has sent down an edict that, due to budgetary
shortfalls, we should try to conserve power.  Actually that's not
such a bad idea in any case.

So far I've done pretty well with the AMD based desktops, both
under linux and Windows XP.  Drops of 12C are typical at idle
and it doesn't affect normal operation adversely. Well, if I
really push the limit sound and video become a bit jerky,
but it's possible to have smooth sound and video and significant idle
power savings.  (Not sure yet exactly how much in watts since the
kill-A-watt has not yet arrived.)  No attempt was made to spin down
the disks or go into that sort of standby - this is for saving
power when the user is just staring at the screen or typing slowly.
This isn't throttling either - that reduces power consumption when
the processor is busy but seems to do nothing when it is
already idle. Also throttling tends to make machines run very
badly.  More details for various processors here (this is a very
early version):

  http://saf.bio.caltech.edu/saving_power.html

Now the bad news, no joy so far with the Tyan S2466N-MPX nodes in
the beowulf.  These have single Athlon MP 2200+ processors, so
no problems with SMP, and use a vanilla 2.6.8.1 kernel.  Unfortunately
starting athcool on them did absolutely nothing to lower the
temperature.  Using athcool to flip the bits off and on didn't raise
the temperature either - it just wasn't doing anything.

This gives a pretty good clue why:
 
 %  modprobe processor
 %  cat /proc/acpi/processor/CPU0/info
 processor id:            0
 acpi id:                 0
 bus mastering control:   no
 power management:        no
 throttling control:      no
 limit interface:         no
 
 /proc/acpi/processor/CPU0/power
 showed that only C1 was supported.  On the ASUS boards both C1 and
 C2 were present.

So my question for this group is, has anybody managed to get
a Tyan S2466N-MPX to use the lower power idle mode?  Is this just
a case of upgrading to a newer Kernel, changing some BIOS
setting , or is this yet another broken feature of the
S2466N-MPX (along with WOL)?

Note that the BIOS has ACPI set to YES and "power savings" set
to disabled.  The latter was set that way because I did NOT
want the nodes going into standby or "auto suspend".  The other
modes listed are "customized", "maximum power savings", "maximum
performance" - none of which are defined.  It may
be though that this must be set to "customized" and the standby
and auto suspend timeouts set to off in order for the low
power idle mode to work.  No way to figure that out from the 
documentation (sic). All of these nodes are currently in use
in the cluster, so it's a bit hard to experiment on them
at this time.  Hopefully one of you has already been through
this and has some answers.

Thanks,

David Mathog
mathog at caltech.edu
Manager, Sequence Analysis Facility, Biology Division, Caltech